1. Field of the Invention
The present invention relates to a coordinate reading device and a coordinate input device.
2. Description of the Related Art
Various types of coordinate reading device and a coordinate input device have been proposed.
FIG. 1(a) is a configuration of a conceivable coordinate reading device and a conceivable coordinate input device. The conceivable coordinate reading device includes: a table 91, a scanning circuit 92, and a detection circuit 90. The tablet 91 is provided with a plurality of X sense coils (conductive loop wires) X1 to Xm and Y sense coils (conductive loop wires) Y1 to Yn. The X sense coils X1 to Xm are for detecting X coordinates of a pen (coordinate input device) 400, the Y sense coils Y1 to Yn are for detecting Y coordinates of the pen 400. The scan circuit 90 is for serially scanning the sense coils X1-Xm and Y1-Yn on the tablet 91. The detection circuit 90 is for calculating the x and y coordinates of the pen by detecting induction signals generated at the sense coils X1-Xm and Y1-Yn.
The pen (coordinate input device) 400 includes a coil 401 that generates an alternating magnetic field. When the pen 400 contacts the tablet 91, some sense coils that are located near to the pen 400 generate induction signals 97 due to magnetic coupling with the alternating magnetic field from the coil 401. The induction signals 97 are inputted into the detection circuit 90. The induction signal 97 are amplified at an amplifier 93 and then its amplitude is detected at an amplitude detection circuit 94. Next, and A/D conversion circuit 95 converts the measured amplitude into digital values, and outputs the digital values to a CPU 96. The CPU 96 calculates the positional coordinate of the pen 400 based on the inputted digital values from the A/D conversion circuit 95. For example, the CPU 96 may refer to a coordinate table that stores data indicative of a relationship between a plurality of digital values and coordinate positions. The CPU 96 selects a positional coordinate that corresponds to the digital values presently inputted from the A/D conversion circuit 95.
Japanese Patent-Application Publication (Kokai) No. HEI-5-233127 discloses a coordinate reading device for a plurality of different type pens. Each pen transmits a code train that includes attribute information indicating attributes of the pen. The coordinate reading device detects the attribute information in the signal.
FIG. 1(b) is a timing chart showing an example of the code train transmitted from the pen. The code train G includes ten bits; two start bits, seven bits indicating pen attribute information, and a single stop bit. The code train G is superimposed on an alternating magnetic field from the pen in accordance with an operation clock F and then outputted.
In the coordinate reading device, the sense coils generate signals to response to the alternating magnetic field transmitted from the pen. The coordinate reading device reads the code train G that is superimposed in the generated signals, and detects the pen attribute information.
According to this method proposed by the publication, however, the coordinate reading device cannot recognize the pen attribute information unless it receives the code train G over a plurality of periods from the start bit to the stop bit.
Also, the coordinate reading device can not recognize the pen attribute information unless the operation clock of the pen is synchronized with the operation clock of the coordinate reading device.
Further, if detection by the sense coils is started somewhere between the start bit and the stop bit, then the coordinate reading device has to wait until the next start bit, and receive the entire code train from the start bit to the stop bit, or will not be able to detect pen attribute information. Thus, it takes a great deal of time to determine the pen attribute information.
Japanese Patent-Application Publication (Kokai) No. HEI-7-160400 discloses another coordinate reading device and a pen (coordinate input device). According to this publication, the pen generates an alternating magnetic field, whose frequency changes according to color of ink in the pen. The pen includes a switch that enables changing the frequency of the alternating magnetic field in accordance with the ink color. The coordinate reading device recognizes the color of the ink by detecting frequency of the alternating magnetic filed outputted from the pen.
In the configuration proposed by this publication, however, the coordinate input device (pen) switches frequency in accordance with the ink color. The coordinate reading device detects the ink color according to the received frequency. It is impossible for the pen to transmit values that consecutively change, such as pressure, at which the pen is pressed against the writing surface of the coordinate reading device. Also, because only a certain number of frequency bands can be used, this configuration can use frequency to designate only a limited number of attributes, that is, the ink color.
Japanese Patent-Application Publication (Kokai) No. HEI-5-274079 discloses a coordinate input device (pen) which includes a marker portion and a case portion. The marker portion is detachably attached to the case portion, and includes a coil and an ink tank filled with ink. The marker portion is used to draw character and figures on a white board using the ink in the ink tank. The case portion includes a battery and a signal tuning circuitry for producing signals to cause the white board to detect the position of the pen. When the ink in the marker portion runs out, then the marker portion is detached from the case portion and is discarded. A new marker portion filled with ink is then attached to the case portion in its place. With this configuration, the battery and the circuitry in the case portion can still be used, so running costs are low. However, the only information the white board obtains from the tuning unit is the position of the input unit on the board.
In view of the above-described drawbacks, it is an objective of the present invention to provide an improved coordinate input device which is capable of transmitting information so that the coordinate reading device can distinguish the information in a short period of time, and to provide an improved coordinate reading device which is capable of distinguishing information, transmitted from a coordinate input device, in a short period of time.
It is another objective of the present invention to provide an improved method for communicating information so that an information receiving side can distinguish the information in a short period of time.
It is another object of the present invention is to provide an improved coordinate input device which is capable of transmitting information indicating a variety of attributes and consecutively-changing values, and an improved coordinate reading device which is capable of detecting information indicating a variety of attributes and consecutively-changing values.
It is still another objective of the present invention to provide an improved coordinate input device wherein a single case portion can be used with a plurality of different marker portions with different colors, wherein the marker portions can be exchanged simply and easily, wherein the characters drawn on the board will properly match ink color information transmitted to the coordinate reading device.
In order to attain the above and other objects, the present invention provides a coordinate reading system, comprising: a coordinate input device, the coordinate input device including: a coil generating an alternating magnetic field; an angle-modulation portion that modulates the alternating magnetic field in an angle modulation to thereby successively change an angle state of the alternating magnetic field into a plurality of different states in a plurality of successive time durations, with a length of at least one time duration corresponding to desired information; and a coordinate reading device, the coordinate reading device including: a main body having a surface defining a coordinate of the coordinate input device; a plurality of wires provided to the main body, each wire generating an electric signal in response to the alternating magnetic field; a coordinate detection unit that calculates the coordinate of a position of the coordinate input device based on the amplitude of the generated electric signal; and an information detection unit that demodulates the generated electric signal to detect the length of the at least one time duration, thereby determining the desired information.
A length of a single modulation period, which is equal to the total length of all the plurality of time durations, may correspond to the desired information. A duty ratio, which is equal to a ratio of a length of one time duration relative to the total length of all the plurality of time durations, may correspond to the desired information.
The angle-modulation portion may include a frequency modulation portion that modulates the alternating magnetic field in a frequency deviation modulation to successively modulate the alternating magnetic field into a plurality of different frequencies in a corresponding plurality of time durations, with a length of at least one time duration for at least one frequency corresponding to the desired information.
The coordinate input device may further have a consecutive detection unit that consecutively detects a characteristic of the coordinate input device. In this case, the length of at least one time duration for at least one frequency may have a consecutively-changing value indicative of the consecutively-detected characteristic of the coordinate input device.
The frequency modulation portion in the coordinate input device may include: a signal production portion that produces a signal that repeatedly changes its amplitude in a modulation frequency, the amount of the modulation frequency indicating the desired information; and a modulation portion that subjects the alternating magnetic field to the frequency modulation by using the produced signal. The coordinate input device may further include: an ink cartridge that includes a tank storing ink, the desired information indicating color of the ink; and a case portion that detachably houses the ink cartridge. In this case, at least a part of the signal production portion may be mounted to the ink cartridge.
According to another aspect, the present invention provides a coordinate input device, comprising: a coil generating an alternating magnetic field; and an angle-modulation portion that modulates the alternating magnetic field in an angle modulation to thereby successively change an angle state of the alternating magnetic field into a plurality of different states in a plurality of successive time durations, with a length of at least one time duration corresponding to desired information.
According to a further aspect, the present invention provides a coordinate reading device reading a coordinate of a position of a coordinate input device, the coordinate reading device comprising: a main body having a surface defining a coordinate of the coordinate input device, a plurality of wires provided on the main body, each wire generating an electric signal in response to an alternating magnetic field from a coordinate input device, the alternating magnetic field being modulated in an angle modulation so that an angle state of the alternating magnetic field is successively modulated into a plurality of different states in a plurality of successive time durations, with a length of at least one time duration corresponding to desired information; a coordinate detection unit that calculates the coordinate of a position of the coordinate input device based on the amplitude of the generated electric signal; and an information detection unit that demodulates the generated electric signal to detect the length of the at least one time duration, thereby determining the desired information.
According to another aspect, the present invention provides an information communicating method, comprising the steps of: generating a carrier wave; modulating the carrier wave in an angle modulation to thereby successively change an angle state of the carrier wave into a plurality of different states in a plurality of successive time durations, with a length of at least one time duration corresponding to desired information, and transmitting the carrier wave; receiving the carrier wave by producing an electric signal whose angle state corresponds to that of the carrier wave; and demodulating the carrier wave to detect the length of the at least one time duration, thereby determining the desired information.